1. Field of the Invention
When phenol is manufactured by cleavage of cumene hydroperoxide, a rough phenol is obtained, which has to be rectified by hydrodistillation or by extractive distillation. In either process, two distillation columns are used. In the upstream (or first) column, at the top, are separated foreign matters, mostly a light cut, consisting of mesityl oxide, hydroxyacetone, cumene, alpha-methylstyrene, 2-methyl-benzofuran and other organic substances, which are present (as impurities) in the pure phenol; and in the downstream (or second) column, the pure phenol is distilled. The purge obtained from the top of the first column contains phenol, in a concentration from 20% to 90% by weight, usually from 50% to 80% by weight. The phenol contained in the purge of the first column can be recovered, as is known, by salification with a strong base, for instance, caustic soda; with the resulting sodium phenate, remaining dissolved in the aqueous phase, subsequently acidified with an acid such as H.sub.2 SO.sub.4, H.sub.2 CO.sub.3 or other similar acids, thereby containing free phenol. To obtain a complete (or substantially complete) shifting of phenol to the aqueous phase, in the form of a salt, it is necessary to operate with an excess of base and, when NaOH is used as a base, the excess usually amounts to a quantity ranging from 1% to 30% of the maximum amount convertible to sodium phenate. Therefore, consumption of base is a considerable burden of the known process.
2. Discussion of the Prior Art
European patent No. 28522 suggests, as an alternative process, the recovery of phenol from the purge of the first column by means of steam distillation. However, in this suggested process the costs connected with the use of steam are quite dear and are not neglectable.
As a matter of principle, it would be possible to recover phenol by means of an extraction with H.sub.2 O this expedient would allow the avoidance of the use of NaOH or steam and the resultant disadvantages associated with each. However, the distribution coefficient of phenol between the aqueous and organic phases in the purge of the first column would require the feeding of a considerable water amount to the plant, which would result in an increase of the power (and reactants) consumption. In this case, the cost, on the whole, would be even higher than the cost arising from the recovery by means of salification with NaOH.
The applicants have now found a method which permits the recovery of phenol from the rectification purge in a very simple manner and with yields similar to those obtainable by use of salification with NaOH or from the steam distillation processes described above, while avoiding any consumption of NaOH or of steam.